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E. Guaguere - J. Declercą

Yiral dermatoses

Viral dermatoses are a developing field in feline dermatology. They are underdiagnosed because of difficulties in identifying the causal virus, but new investigative procedures (e.g. electron microscopy, immunohistochemistry and viral amplification) have enabled these new dermatoses to be characterised. An understanding of them is important as they enter into the differential diagnosis of many different conditions. They also represent a major zoonotic risk for man.

Powirus infection

Aetiopathogenesis

Poxvirus infection is a viral dermatosis caused by cowpox virus, an orthopox virus, and has been reported in many species, notably the cat Seen for the first time in Great Britain \ poxvirus infection is reported regularly in the Netherlands \ Belgium, Austria ⁵, Germany ⁶, Italy ⁷ and now France ⁸. Not all strains of poxvirus isolated in the cat are identical and they seem to vary according to their geographical origin. In Great Britain, the virus isolated in the cat is the same as the cowpox identified in other species. However, this has not been verified in other countries⁹.

In almost every case, poxvirus infection has been seen in rural hunting cats ^U9. Infection occurs mainly through contact with rodents (e.g. voles and field mice) and sometimes with cattle. The increased incidence in summer and autumn (very pronounced in Great Britain) relates to when these rodents are most actiye and also their breeding season ⁹. The route of infection of cowpox virus is percutaneous and sometimes oronasal ^9,l°. The latter route is responsible for a milder form of the disease, which is why cats in contact with an alfected cat will sometimes seroconvert, but rarely show clinical signs of infection. After infection, the virus undergoes local replication and produces the primary lesion. It then spreads via the lymphatics to cause multiple secondary lesions⁹.

Clinical features

Dermatological signs are characterised firstly by a solitary lesion on the head, neck or forelimbs '•^{8 n}. This lesion is an erythematous macule which ulcerates rapidly (Fig. 7:1). Within about 10 days, many secondary pruritic lesions, including macules, papules and nodules (0.2-2 cm in diameter), appear all over the body (Fig. 7 : 2,3). They are initially erythematous, becoming ulcerated. About 20% of cats have ulcerations in the orał cavity and on the tongue (Fig. 7 : 2)⁹. Systemie signs may be present. These include depression, anorexia, pyrexia, conjunctivitis and respiratory signs⁹.

In most cases, these secondary lesions resolve spontaneously within 3-8 weeks⁹. Secondary bacterial infection or concurrent FIV infection can lead to development of systemie signs, including pneumonia which may sometimes prove fatal⁹.

Laboratory tests

Impression smears, stained with May-Grunwald-Giemsa may reveal the intracytoplasmic eosinophilic inclusion bodies characteristic of pox viruses (Fig. 7 :4), but this procedurę should only be undertaken by a very competent cytologist⁵-⁶.

Histopathological examination of skin biopsies, taken from the margin of recent lesions, reveals hydropic degeneration of keratinocytes and cells of the follicular outer root sheath, the presence

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